The present invention generally relates to ink printing technology, and more particularly to a specialized ink containment unit for use in an ink delivery system which is resistant to the corrosive effects of ink, prevents air entry into the ink, and avoids the evaporation of volatile ink components therefrom. As a result, the overall longevity and operational efficiency of the entire ink delivery system is improved.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure which is conventionally characterized as a "printhead"Selective activation of the resistors causes thermal excitation of the ink materials stored inside the reservoir chamber and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. No. 4,500,895 to Buck et al.; U.S. Pat. No. 4,794,409 to Cowger et al.; U.S. Pat. No. 4,509,062 to Low et al.; U.S. Pat. No. 4,929,969 to Morris; U.S. Pat. No. 4,771,295 to Baker et al.; U.S. Pat. No. 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, U.S. Pat. No. 4 (August 1988), all of which are incorporated herein by reference.
The ink delivery systems described above (and other systems using different ink ejection devices as discussed below) typically include an ink containment unit (e.g. a housing or vessel) having a self-contained supply of ink therein in order to form an ink cartridge. In a standard ink cartridge, the ink containment unit is directly attached to the remaining components of the cartridge to produce an integral and unitary structure wherein the ink supply is considered to be "on-board". However, in other cases, the ink containment unit will be provided at a remote location within the printer unit, with the containment unit being operatively connected to and in fluid communication with the printhead using one or more ink transfer conduits. These particular systems are conventionally known as "off-axis" printing units. The present invention shall be applicable to both of these designs, and may likewise be used in connection with ink printing devices that use non-thermal-inkjet technology. Accordingly, while the claimed invention shall be described herein with primary reference to thermal inkjet printing systems, it is likewise applicable to any ink delivery apparatus which employs a housing or vessel containing a supply of ink therein which has corrosive capabilities and volatile ink components.
An important consideration in the development of an ink containment unit for use with a thermal inkjet (or other type) of printing system is the ability of the containment unit to avoid substantial air introduction into the ink supply and printhead. Excessive air introduction (when reaching a critical volume) can cause a loss of system back-pressure which will typically result in operational failure of the ink ejection components and reduce overall printhead life. It is also important to prevent the evaporation of volatile components from the ink supply, with these components including water and organic solvents such as 2-pyrrolidone, 1,5-pentanediol, N-methyl pyrrolidone, 2-propanol, 2-ethyl-2-hydroxymethyl-1,3-propanediol, cyclohexanol, and others as discussed in considerable detail below. Solvent evaporation can result in a chemical deterioration of the ink supply which will reduce overall print quality and can cause premature failure of the ink delivery printhead. Accordingly, these factors must be carefully considered in any ink delivery system regardless of whether the ink containment unit (e.g. housing or vessel) is of the "on-board" variety or remotely positioned from the printhead.
Many ink cartridge units have employed rigid, thick-walled ink storage housings for containing ink therein which is present in "free flowing", unconstrained form or held within a multi-cellular foam-type member. Representative ink cartridge units which employ these types of ink containment systems are illustrated in U.S. Pat. Nos. 5,185,614 and 5,168,285 which are incorporated herein by reference. The housing units described above (which traditionally have effective gas/vapor barrier properties) are constructed from a number of different materials including glass, polytetrafluoroethylene (Teflon.RTM.), stainless steel, or various plastics including polystyrene and polycarbonate compositions. While these materials typically have good barrier capabilities as previously noted, their rigid and "non-collapsible" character requires the introduction of air or other gaseous materials into the system when ink delivery occurs to overcome negative pressure effects which can cause the interruption of ink flow.
Other ink delivery systems have employed flexible ink containment structures in the form of bags or bladders constructed of film-type compositions which are typically retained inside a rigid housing. The flexibility of these ink containment structures allows them to deliver ink materials without the need to introduce air and/or other gases into the system under consideration. Representative ink cartridge units which employ this type of "flexible" ink containment unit are illustrated in U.S. Pat. Nos. 5,153,612 and 5,280,300, as well as co-pending (and co-owned) Pending U.S. application Ser. No. 08/869,446 which are all incorporated herein by reference.
While flexible, bag-type systems offer numerous advantages, they are nonetheless subject to undesired air leakage into the ink supply and ink evaporation problems. In addition to air leakage and evaporation problems, these systems are also subject to damage caused by the corrosive effects of ink materials normally used in modern printing systems. As a result, film deterioration (and ink leakage) can occur, with these problems being caused by a number of "corrosive" ink ingredients including but not limited to one or more of the organic solvent materials listed above, as well as various acidic dye compounds.
A substantial need has therefore existed for an ink containment unit which can be produced in flexible form, yet is capable of strong resistance to ink corrosion problems, prevents air from entering the ink supply, and avoids the evaporation of volatile ink components including organic solvents and water. The present invention described below solves these problems in a unique and highly effective manner. Specifically, a novel film product, an ink containment vessel produced therefrom, an ink delivery system using the vessel, and an ink evaporation/air entry control method are all disclosed which provide many important benefits. These benefits include (1) the avoidance of ink corrosion problems and ink leakage from the system; (2) the prevention of air entry into the ink supply and printhead; and (3) the control of ink evaporation and losses of volatile ink components. As a result, high levels of operating efficiency, print quality, and longevity are maintained in connection with the ink delivery system under consideration. These and other benefits associated with the claimed invention (as well as the specific details thereof) shall be discussed in considerable detail below.